Society as a whole is moving towards sustainable, renewable, and clean energy sources. Because of on-demand energy requirement the high density energy storage and power delivery systems play a larger role in our lives. They provide solar power in night, wind power when there is no wind, and enable electric cars go longer distances between charging. There continues to be a strong need for energy storage system with high power and energy density to meet the higher requirements of portable electronics to hybrid electric vehicles. Similarly, there is a continuous need to increase energy consumption efficiency directly via lower loss waist energy as well as by means of lighterweight transportation modes and mobile devices. As a part of this trend and further more a growing trend of mobile electronics, there are major attempts to miniaturize electronic devices and their components.
Developments over the past decade of composites containing conductive or very high-permittivity nanoparticles [e.g., Cu, Ag, graphene, BaTiO3, calcium copper titanate (CCTO)] with sizes on the order of 100 nm or less, referred to as nanodielectric or nanocomposite dielectrics, are showing that dielectric materials with certain desired properties can be generated. The observation of potential benefits associated with nanodielectric materials is relatively recent. Since the 1990s, considerable effort has been conducted with respect to nanocomposite dielectric materials utilizing a broad class of polymeric matrices (e.g., polyethylene of assorted densities, cross-linked polyethylene, epoxies, polyimides, polyacrylates, polycarbonates, silicones) that have incorporated a number of different inorganic phases, such as metals, silicates, aluminates, magnesiates, titanates, and a variety of clays. Reported high-permittivity values achieved by such nanodielectric materials have been in the permittivity (εr) range of 10 to the high 103, the later being defined as “giant” and “colossal” permittivities.
Materials such as doped barium titanates and CCTO that are polarized are reported to provide εr values in the range of 104 to 105 but are hard and expensive to be made and processed in conjunction with delicate electronic devices. Nevertheless, Ceramic multilayer capacitors with barium titanate as the ceramic dielectric medium are currently the state of the art in the passive capacitor component market. CCTO, having one order of magnitude higher permittivity has not capture a large market share yet, due to the cost of high quality powders and their processing into a viable ceramic component. Once mixed with polymers, the values for these high permittivity materials is dropped by 2 to 3 orders of magnitude, even if added as nanoparticles and in high volume fraction.
There are several significant problems of such highly desired nano dielectric materials—(a) is homogeneous morphologies of such nanocomposites are difficult to process (b) they reach percolation at relatively low volume fraction they pass a percolation threshold and (c) their electrical conductivity increases beyond the values desired for storing electric energy. In other words, they become highly leaking. Attempts to prevent such high leakage are reported but do not provide yet high satisfactory combinations at the very high permittivity range. Furthermore, processing at the industrial level of such nanocomposites is not as reliable as doing it at small lab scales.
Incorporation of graphene into polymeric and ceramic hosts is a new trend in advancing materials for electronic applications. Many of these attempts are associated with the desire to increase the conductivity of the polymers and the ceramics aside from improving their mechanical performance. Increased conductivities of such composites are reported even at values of 1 to 5 vol % of graphene. In all these cases, the graphene or its precursor—graphene oxide—are physically mixed with polymers and ceramic hosts via the use of pre-synthesized graphene or graphene oxide, yet even at a single layer stage (i.e., with a sub-nanometer thickness) their planar dimension is in the microrange of 0.5 to 10 μm. Graphene oxide is now the new trend in making composites containing homogeneously dispersed graphene platelets. The graphene oxide serves as a practical intermediate that is easily suspended in water and certain organic solvents and this subsequently aids in achieving improved homogeneity of the composite, provided that after the blending it is possible to convert back the graphene oxide to graphene (e.g., by exposure to a gasous reducing agent such as hydrazine, which is very toxic.) Although graphene, organically modified graphene and graphene oxide are traditionally defined as “nanoparticles”, it should be noted that in their manufactured stage the nanodimension is just in the thickness of the layer. In contrast, their plane dimensions are in the range between 500 to 10,000 nm, which again reduce their practical potential and lead to percolation phenomena at very low concentrations.
Relevant art: WO 2012/006416; U.S. Pat. No. 8,574,681.